1. Field of the Invention
The field of the present invention relates:
generally to flexible couplings for rotary shafts transmitting torque via a flexible element;
more particularly to flexible couplings for rotary shafts transmitting torque via a flexible element facilitating angular misalignment; and
most specifically to the use of sleeve inserts in flexible coupling of rotary shafts with torque transmission via a flexible element that facilitates angular misalignment.
2. General Background
It is considered that the basic, fundamental, purpose of a flexible shaft coupling is the transmission of torque between drive and driven shafts possessing a small degree of angular misalignment between substantially aligned rotational axes. In this context it is next considered that flexible shaft couplings are used in a huge range of applications which can perhaps best be demarcated by one simple opposition between larger, dedicated, applications and smaller, variable, applications. The coupling of a drive shaft to a knuckle joint on a driven wheel of an automobile is considered exemplary of the first category. Other examples of similarly large, dedicated, applications include coupling of an airplane propellor or helicopter rotor to a power drive shaft. Opposed to this are flexible shaft couplings which are generally available with different bore sizes for coupling rotary shafts in precision power transmission, positioning control, and smaller power transmission devices including but not limited to: encoders, resolvers, DC tachometer generators, precision potentiometers, stepper and servo motors, XYZ tables, robotics, optics, laboratory, medical and business machines.
It is noted that in the second category flexible shaft couplings are typically used as xe2x80x98off the shelfxe2x80x99 components in the building of machines or for coupling the driven shaft of a device to the shaft of an electric motor for a temporary, unique, or otherwise various purpose. In either case the couplings are purchased in accordance with the diameter of the shafts concerned. The shafts, however, are not always of the same diameter. And if a flexible shaft coupling having the two different diameter shaft bores desired is available the expense may be considerable for what essentially must be a xe2x80x98specialxe2x80x99 run for the flexible coupling manufacturer. Otherwise a flexible coupling having one bore which fits the smaller shaft is commonly used and the other bore is machined out to the larger diameter required.
It is further considered that xe2x80x98miniaturexe2x80x99 shaft couplings intended for use in precision power transmission, positioning control, and smaller power transmission devices including but not limited to: encoders, resolvers, DC tachometer generators, precision potentiometers, stepper and servo motors, XYZ tables, robotics, optics, laboratory, medical and business machines are more economically molded in plastic than machined in metal, and in this case a xe2x80x98special runxe2x80x99 of flexible couplings having shaft bores which are not xe2x80x98stockxe2x80x99 is impractical as this requires a whole new set-up with a new mold, and a separate production run, as opposed to simply altering the bore concerned at the end of a routine, standard stock size, production run for just the number of units ordered in which case only the time necessary to make the single tool adjustment is incurred as an additional expense.
Another basic distinction, based upon the economics of manufacture concerned, is hence recognized between molded plastic flexible couplings and machined metal rotary shaft couplings. Molding is more economic in volume production and machining is more economically accommodative of variations, particularly with respect to bore diameter, as his is determined simply by the position of a tool during the routine manufacturing process while molding a different bore requires a whole new set-up with a new mold.
U.S. Pat. No. 949,189 issued to Hugo Lentz discloses a xe2x80x98universal couplingxe2x80x99 using a rectangular cross section xe2x80x98bushxe2x80x99 or sleeve which fits into the rectangular bore of the hub of a xe2x80x98rotary cylinderxe2x80x99 and into which a shaft having at least two exterior parallel opposed surfaces contacting interior opposed parallel surfaces of the xe2x80x98bushxe2x80x99.
The other two opposed parallel surfaces can also make contact, as shown in FIG. 7, but it is preferred that these surfaces have a xe2x80x98swellxe2x80x99 or outward smooth curved enlargement which contacts the bush interior walls and holds the shaft by tightening two set screws behind the xe2x80x98swellsxe2x80x99.
French Patent 1306123 issued to M. Antelme discloses a coupling with a solid elastic body with two opposed blind hexagonal cavities into which a hex nut with a smooth bore is located with a radial pin through apertures in the coupling body and the nut.
A long bolt is apparently threaded through a tapped aperture through the middle of the pin for fixing the depth of the pin which, although shown to be smooth, clearly engages a tapped aperture in the nut and has a slot 10 on the end which would allow rotation with a flat blade screwdriver. The pin evidently passes through a transverse aperture through a shaft located in the bore of the nut or hexagonal insert and the long bolt could attach the shaft to the pin.
U.S. Pat. No. 3,395,552 issued to Hauser, Jr. discloses a flexible coupling having a stiff sleeve 8 fitted into an interiorly xe2x80x98serratedxe2x80x99 or splined bore of a flexible sleeve which is longer and is connected at either end to a shaft hub, 2, 4, by a pin 11 through opposed apertures 12, 13 through the hub and ends of the flexible sleeve which reduces shock transmission and accommodates slight shaft misalignment while the stiff sleeve insert provides dampening at resonant frequencies.
Great Britain Patent 1 283 723 issued to Mayerjak discloses, as clearly seen in FIG. 5, a flexible coupling using a rubber sleeve between the exterior surface of a small diameter tubular member and the interior surface of a larger diameter tubular member which are mechanically connected by sets of arms: xe2x80x9cFinally, in the embodiment described . . . the use of an elastomeric bushing 62 between the drive and driven shafts has the result of increasing the natural frequency of the overall coupling, and . . . provide a fail safe restraint in the event of failure of one or more of the flexing elements.xe2x80x9d (Page 3, lines 35-49)
Soviet Union Patent 1106558 issued to the KRAMA Mechanical Engineering Research Institute discloses a xe2x80x98universal hingexe2x80x99 or coupling for two rotary shafts, one having a split blade held by a xe2x80x98frictional insertxe2x80x99 in a bore of the other shaft which is held in an outer sleeve with a frictional insert. The outer sleeve contacts the exterior of the first shaft directly. The frictional inserts have curved exterior surfaces which apparently provide for two axes of rotation in accommodation of angular shaft misalignment.
U.S. Pat. No. 4,560,364 issued to Cohen discloses a xe2x80x98fail-safe improvement for a flexible couplingxe2x80x99 using a xe2x80x98plugxe2x80x99 which is threaded into one shaft and has a flange for retaining a tubular section of the second shaft in connection with the first if the primary, outward double wall flange, coupling fails. The plug is provided with a xe2x80x98headxe2x80x99 shown as a hex which facilitates tightening.
Because smaller flexible shaft couplings typically used as xe2x80x98off the shelfxe2x80x99 components are often desired for applications in which two different diameter shafts must be coupled and because flexible shaft couplings having different shaft bores are often not readily available, particularly in molded plastic xe2x80x98miniaturexe2x80x99 flexible shaft coupling suited for economic precision power transmission, positioning control, and smaller power transmission, it is considered desirable to be able to economically reduce the bore of a flexible shaft coupling, particularly the bore of a molded plastic xe2x80x98miniaturexe2x80x99 flexible shaft coupling suited for economic precision power transmission, positioning control, and smaller power transmission which, because it is molded, cannot have a bore diameter economically altered during the routine manufacturing process. And while a variety of hollow, sleeve type, inserts into which shafts are fitted are known which fit the bore of a flexible coupling none have the purpose or capability of accommodating various shaft diameters as none effect a reduction of a flexible shaft coupling bore diameter which could be used without the insert with a larger diameter shaft.
A need is hence discerned for an economic means of reducing a shaft bore of a flexible shaft coupling, particularly the bore of a molded plastic xe2x80x98miniaturexe2x80x99 flexible shaft coupling suited for economic precision power transmission, positioning control, and smaller power transmission in various applications in which flexible shaft couplings are used as xe2x80x98off the shelfxe2x80x99 components and the manufacturing process prohibits economic variation of bore diameter during routine production.
The primary, encompassing object of principles relating to the present invention, is the provision of a system for the accommodation of multiple shaft diameters by a single flexible rotary shaft coupling.
A first auxiliary object of the principles relating to the present invention is the provision of a system for flexible coupling of a driven shaft having a different diameter than the drive shaft using purchased components without enlargement of a coupling bore by subsequent machining.
An ancillary object of the principles relating to the present invention is the provision of an economic system for flexible coupling of a driven shaft having a different diameter than the drive shaft in precision power transmission, positioning control, and smaller power transmission devices.
Another ancillary objective of the principles relating to the present invention is the provision of an economic system for flexible coupling of a driven shaft having a different diameter than the drive shaft in precision power transmission, positioning control, and smaller power transmission devices which utilizes molded plastic components.
A second auxiliary object of the principles relating to the present invention is the provision of an economic system for flexible coupling of a driven or drive shaft having various diameters.
Other ancillary objectives of the principles relating to the present invention include the provision of an economic system for flexible coupling of a driven or drive shaft having various diameters which is simple and easy to use and provides adequate torque transmission characteristics.
In achievement of the above stated objectives it is suggested that a sleeve insert be utilized in reduction of an effective bore of a flexible shaft coupling and that the sleeve insert and be molded in plastic. It is suggested that a clamp collar effecting compression through the sleeve insert in engagement with a shaft be utilized and hence that the sleeve insert be radially compressible. It is considered that thermoplastic generally possesses excellent resilience, compressibility, and surface adhesion in comparison with metal and that a molded plastic insert is hence inherently both compressible and better suited to the transfer of torque through surface contact.
In facilitation of diameter reduction of the sleeve insert during radial compression it is suggested that a longitudinal interruption of the circumferential extension of the sleeve insert be effected with a longitudinal slot through the wall of the same. And it is suggested that congruent longitudinally uniform but radially non-uniform configurations be used for the sleeve insert and the bore of the flexible coupling to provide additional torque capacity.
One or more radially flattened longitudinal sides to both the exterior surface of the sleeve insert and the bore of the flexible coupling is suggested as one class of longitudinally uniform, radially non-uniform, configurations considered suitable. Splined surfaces are also suggested as suitable configurations as is the use of one or more matching keys and key ways.
It is further suggested that the interior surface of the sleeve insert be substantially cylindrical, in order to conform to the greatest majority of rotary shafts commonly utilized in precision power transmission, positioning control, and smaller power transmission devices, except for any longitudinal interruption by use of a slot through the wall of the sleeve insert.
The flexible coupling possesses at least one longitudinal slot through the wall of the same which is partially closed in the application of compression upon the shaft through the radially compressible sleeve insert by the exertion of transverse compression across the slot effected by the tightening of a threaded fastener which bridges the slot. As compression upon each shaft is required use of a single longitudinal slot entails that both threaded fasteners bridge the same, full length, longitudinal slot. If this slot is extended across both wall, effectively dividing the body of the flexible coupling into two bilateral portion, two additional threaded fasteners are required in a simple clamp arrangement which is opposed to a clamp collar wherein the coupling body is one piece.
If two longitudinal slots are utilized the threaded fasteners can be disposed in other dispositions. The threaded fasteners, and much shorter than full length longitudinal slots, can be radially opposed rather than aligned or offset from each other by ninety degrees. The use of shorter than full length longitudinal slots, moreover, facilitates the use of more complex configurations including use of one or more axially suspended discs as described in U.S. patent application Ser. No. 10/152,291 entitled xe2x80x98Integral Thermoplastic Body Flexible Shaft Couplingxe2x80x99. This specifically suggested configuration accommodates a full degree of angular misalignment between shafts per disc axially suspended by two radially perpendicular pairs of opposed longitudinal arm extending across an axially open core and provides good torque transmission characteristics.
It is hence also recommended that the body of the flexible shaft coupling be molded plastic although this is not necessary and that stainless steel nuts and bolts be used for the threaded fasteners, particularly for miniature flexible coupling systems intended for precision power transmission, positioning control, and smaller power transmission devices. Other specific suggestions in embodiment of the principles relating to the present invention may be appreciated with a reading of the detailed description following, especially if conducted with reference to the drawings attached hereto, and briefly described immediately below, utilizing the reference numerals common to both in identification of elements further catalogued in the nomenclature following this.